In exploring for oil under the sea, surveyors onboard a ship typically deploy air gun cables and streamer cables behind the moving vessel. The air gun cables include a string of acoustic guns which generate acoustic signals which are transmitted into the ocean floor and reflected from rock formations below the ocean floor. The streamer cables are equipped with hydrophones which detect the reflected acoustic energy.
In practice, when it is desired to deploy air gun cable strings from a moving vessel, a tow cable is attached at one end thereof to the vessel and a wingshaped paravane is attached to the tow cable at the other end. The air gun strings are then attached to the tow cable and paid out to the desired position on the tow cable. When underway, the paravane will pull the air gun cable away from the vessel and toward a point perpendicular to the path of the vessel. The paravane thus insures that the air gun cable is stretched out to its full extent and maintained at a constant tension during the surveying operation. The wing shape of the paravane creates an outward force on the paravane along the direction of the tow line connected between the ship and the paravane, and the angle of incidence or attack of the wing-shaped paravane in the water determines its direction and the angle of deployment relative to the path of the vessel.
In existing paravane systems, the lines connecting the paravane to the ship are arranged so that the paravane is maintained in a nonvariable, substantially vertical position in the water. The pull forces created by the paravane angle of attack in combination with the forces created as a result of the wing shape of the paravane thus insure maximum extension from the vessel. Problems with these existing systems has arisen, however, because the paravane have been relatively uncontrollable during normal operation and extremely difficult to tow onboard the towing vessel when the survey is completed. For example, since prior paravanes are normally maintained perpendicular to the tow cable, substantial force must be exerted to bring in the paravane. Further, prior paravanes are difficult to bring onboard from the water without hitting against the tow ship. Moreover, prior paravanes which have fixed attack angles cannot be varied in order to vary the ultimate position of the paravane or the force exerted on the tow cable by the paravane. The present invention obviates those disadvantages by providing an improved handling system for deploying and retrieving air gun tow cables and the attached paravane. The system includes means for selectively controlling the attack angle and movement of the paravane and permits easy retrieval of the paravane and cable once the surveying operation is completed.